Origin and development of legionnaires’ disease

Origin and development of legionnaires’ disease

The term Legionellosis refers to all the serious forms of pneumonia caused by more than 40 species of aerobic bacteria belonging to the genus Legionella. They are ubiquitous microorganisms very present in humid or hot or aqueous environments, the most dangerous of which is Legionella pneumophila, which is responsible for about 90% of all cases of disease.

The disease was first identified following a major epidemic in 1976 in a group of former American Legion fighters (hence the name of the disease) who attended a conference at the Westin Hotel in Philadelphia, USA.

Since then, on the basis of the WHO Guidelines, a system of surveillance of the disease has been activated in many countries. In Italy, for cases of legionnaires’ disease, with DM Salute 15/12/1990, the compulsory notification in class II in SIMI (Sistema Informativo delle Malattie Infettive e diffusive) is foreseen.

Legionella has been isolated in civil and industrial water-sanitary and aeraulic systems of old construction or with inadequate maintenance or, in some cases also from the natural water of rivers, lakes and storage tanks.

The disease develops in two forms of different severity: the actual legionnaire’s disease, which frequently includes an acute form of pneumonia, and Pontiac fever, a much less severe form.

The incubation period usually ranges between 2-10 days and symptoms occur on average between 3-6 days after exposure, initially with fever, chills, headache and muscle pain, followed by dry cough and breathing difficulties which in some cases progress to severe pneumonia.

About 30% of those affected are also affected by diarrhoea or vomiting and about 50% by mental confusion and delirium, with an average lethality rate of 10-15% that exceeds 60% in infants or elderly people and in transplanted or immunosuppressed patients. To date, it has not been demonstrated that the disease can be contracted by drinking contaminated water and direct human transmission seems to be excluded.

Legionnaires’ disease is generally contracted by the respiratory tract, by inhalation or microaspiration of aerosols in which the bacterium is contained. These aerosols are formed through the tiny drops generated by the spray of water, or by the impact of water on solid surfaces. The smaller the droplets are, the more dangerous they are (eg: drops of water with a diameter < 5μ reach more easily the lower respiratory tract and become invasive).

Aerosols that are hazardous to health can be generated by favorable environments, characterized by poor use, maintenance and neglected sanitization, such as, for example:

  • water storage tanks;
  • breakwater of shower taps and shower heads;
  • whirlpools, swimming pools, saunas, Turkish baths;
  • hydro fans, humidifiers, air conditioners, split, fan coils;
  • UTA batteries, cooling towers, evaporative condensers, air treatment systems;
  • irrigation systems for parks and gardens;
  • waste water from hygienic systems.

Risk analysis Drinking water sanitation system

 

Possible risk points Types of risk Preventive action envisaged
Accumulation tank Stagnation and high bacterical load  

Cleaning and disinfection

 
Hot water storage  

a) stagnation, scale, high bacterial count

b) Temperature between 25°C- 45 °C

 

 a) Cleaning and disinfection

b) Temperature > 60°C

 
Cold water storage  

a) stagnation, scale, high bacterial count

b) Temperature between 25°C- 45 °C

 a) Cleaning and disinfection

b) Temperature < 20°C

 
Shower  

a) Stagnation, scale, high bacterial count

b) Temperature between 25°C- 45 °C

 

 a) Cleaning and disinfection

b) Inlet temperature > 50°C
Taps  

a) stagnation, scale, high bacterical count

b) Temperature between 25°C- 45 °C

 

 a) Cleaning and disinfection

b) Inlet temperature > 50°C
Endpoints  

a) stagnation, scale, high bacterical count

b) Temperature between 25°C- 45 °C

 

 Continuous cleaning and disinfection with a specific product

 

Prevention and control of the risk of exposure to legionnaires’ disease

Preventive measures Frequency of interventions
Constant maintenance of hot water at a temperature above 50°C after 1 minute from dispensing.

The hot water in the tank is stored at a temperature of > 60°C/span>

 Continuous
Flush the storage tanks (hot and cold) Weekly
Constant maintenance of cold water at a temperature < 20°C Continuous
Run hot and cold water from taps and showers in rooms that have not been occupied for more than 7 days for a few minutes at least before they are occupied Weekly

(for unoccupied rooms)
Keep showers, shower diffusers and faucet breakers clean and free of scale, replacing them if necessary Quarterly
Regularly clean and disinfect the cooling towers/condensers of the air conditioning units at least twice a year. Six Months
Inspect visible water tanks, cooling towers, AHUs and pipes.

Ensure that all covers are intact and correctly positioned.

 Monthly
Disinfection of the hot water circuit in a continuous manner with the appropriate product Continuous
Empty, descale and disinfect hot and cold water storage tanks and restore operation after thorough washing Annual
Cleaning of water filters in the aqueduct Max quarterly
Water sampling at specific points for the detection of legionella. Six months

Sampling plan for hospitality facilities by size

Medium-sized receptive structure (1-100 rooms)

For each sanitary hot water system, the following samples are taken every six months:

  • General supply from the aqueduct or from the tap closest to the tank(s);
  • Recirculation;
  • Tank bottom(s);
  • at least 3 at representative points
    (i.e. the furthest away in the water distribution and the coldest).

For each cold sanitary water system, the following samples are taken every six months:

  • tank bottom(s) or storage/compensation tanks;
  • at least 2 at representative points (i.e. the farthest in the water distribution and the hottest).

Medium- to large-sized hospitality facility (101-200 rooms)
For each hot sanitary water system, the following samples are taken every six months:

  • general supply from the aqueduct or from the tap closest to the tank(s);
  • recirculation;
  • tank bottom(s);
  • at least 6 at representative points
    (i.e. the furthest away in the water distribution and the coldest).

For each cold sanitary water system, the following samples are taken every six months:

  • tank bottom(s) or storage/compensation tanks;
  • at least 4 at representative points (i.e. the farthest in the water distribution and the hottest).

Large hospitality facility (201-300 rooms)
For each hot sanitary water system, the following samples are taken every six months:

  • general supply from the aqueduct or from the tap closest to the tank(s);
  • recirculation;
  • tank bottom(s);
  • at least 9 at representative points
    (i.e. the furthest away in the water distribution and the coldest).

For each cold sanitary water system, the following samples are taken every six months:

  • tank bottom(s) or storage/compensation tanks;
  • at least 6 at representative points (i.e. the farthest in the water distribution and the hottest).

Methodology and sampling results

Sampling mode

Sampling must be carried out before any disinfection operation or preventive practice is carried out (cleaning and/or disinfection by any method) or at a reasonable distance from its execution (e.g. about 48 hours after the post- intervention system has been put into operation).

The operational protocol to sample is as described in Annex 3 of the “Guidelines for the prevention and control of Legionnaires’ disease Conference State-Regions 2015”.

Results of sampling

If sampling is positive, in addition to what is specified in the checklist, depending on the legionella load found in the bacteriological test, the measures listed in the following tables shall be implemented.

Table 1 – Types of intervention indicated by concentration of Legionella in water systems at risk 

Count

Legionella (UFC/L)

 Required intervention
Up to 100 Check that the current risk control practices are being applied correctly.
Between 101 and 1.000

 

 In the absence of cases:

Verify that the facility has carried out a risk assessment and that the control measures listed in these guidelines are being properly applied.

In the presences of cases:

Verify that the control measures listed in these guidelines are in place, review the specific risk assessment and disinfect the facility.
Between 1001 and 10.000

 

 In the absence of cases:

– If less than 20% of the samples taken are positive, the water system should be resampled, at least by the same positive water dispensers, after verifying that the current risk control practices are correctly applied. If the result is confirmed, a review of the risk assessment shall be carried out to identify the necessary further corrective measures. The water system shall be re-sampled, after corrective measures have been applied.

– If more than 20% of the samples taken are positive, disinfection of the system is necessary and a review of the risk assessment must be carried out to identify the necessary further corrective measures. The water system must be re-sampled, at least by the same positive water outlets.

In the presences of cases:

Independently of the number of positive samples, disinfection of the system and a review of the risk assessment should be carried out to identify the necessary further corrective measures. The water system shall be resampled after disinfection, at least by the same positive water outlets.
Above 10.000

 

 Both in the presence and absence of cases, the system should be disinfected (replacing the positive terminals) and the risk assessment reviewed.
The water system shall be resampled, at least by the same positive water outlets.

Regulatory references

With the Ministerial Decree of December 15, 1990, issued by the Ministry of Health, Legionnaires’ disease is one of the infectious and contagious diseases, which requires reporting. In this regard, the Higher Institute of Health has launched a National Programme of Surveillance of the disease, establishing a National Register of Legionnaires’ disease (DM 07.02.83). The objectives of the Register are to monitor the frequency of legionellosis diagnosed in Italy, identifying any changes in trends, in order to activate appropriate control measures.

  • Legionnaire’s Guidelines State- Regional Conference 2015
  • European Legionnaires’ Disease Surveillance Network (ELDSNet) – Operating procedures 2012
  • Guidelines “Prevention and control of Legionnaires’ disease in the region of reference
  • Legislative Decree 81/08 “Consolidated text on health and safety at work – List of classified biological agents”.
  • Legionella and the Prevention of Legionellosis WHO 2007
  • Guidelines for the definition of technical protocols for predictive maintenance on air conditioning systems Conference State-Regions 2006
  • Guidelines on legionnaires’ disease for managers of tourist and spa facilities 2005
  • European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease – Procedures for responding to travel associated cases of Legionnaires’ disease 2002
  • Legislative Decree 31/01 “Quality of water intended for human consumption” and subsequent amendments and additions
  • U.S. Occupational Safety and Health Administration) “Technical Manual – Legionnaires’ Disease”.
  • ASHRAE Guidelines (American Society of Heating, Refrigerating, and Air-Conditioning Engineers
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